Among the various designs of ordnance delivery devices, there are two extremes. At one end of the spectrum are unguided ordnance delivery devices—those systems for which trajectory is determined by the firing conditions and the environmental conditions of the flight path. At the other end of the spectrum are seven degree of freedom guided ordnance delivery devices—those systems for which trajectory may be modified in flight according to information relating to its actual trajectory and for which translation along each axis, rotation about each axis, and time of impact may be modified by a control system. While guided ordnance delivery devices generally provide the benefits of increased accuracy and precision, the systems required to provide guidance to an ordnance delivery device generally increase the cost of the ordnance delivery device compared with an unguided equivalent.
Guidance systems may take various forms. Such systems may use external information sources such as laser targets, satellite navigation systems, electromagnetic signals, visual data, etc. Such systems may alternatively comprise inertial guidance systems such as linear accelerometers, angular accelerometers, gyroscopes, etc. Such systems may further combine inertial guidance with external information sources in an integrated or independent configuration. Whether a guidance system uses inertial guidance or external information sources, the information obtained may be used to approximate the actual trajectory of the ordnance delivery device. With this approximation, the guidance system may be configured to compare the actual trajectory with the desired trajectory. If the comparison suggests that course correction is necessary, the system may actuate a control surface to modify the actual trajectory.
A variety of control surfaces are generally distinguishable by method of actuation and desired effect. As to methods of actuation, these include extension of a deflector, extension of a fin, extension of a combination of deflectors and fins, selective deformation of a nosecone, rotation of a portion of the control surface, de-rotation of a portion of the control surface, directed ejection of mass, activation of a gyroscope, combinations thereof, and/or the like. As to desired effect, these include imparting a resultant force such that the ordnance delivery device is displaced along at least one of the x-y-z axes, imparting a resultant torque such that the ordnance delivery device is rotated about at least one of the x-y-z axes, imparting a combination of resultant forces and/or resultant torques such that the ordnance delivery device is displaced and/or rotated with respect to at least one of the x-y-z axes, combinations thereof, and/or the like. These methods of actuation and desired effects may be better suited to some ordnance delivery device events than others. For example, assuming that a 7-DOF guidance system is more costly than a 1-DOF guidance system and assuming that some targets are more valuable than others, it may be desirable to reserve the more expensive guidance systems for higher value targets.
Regardless of the method of actuation or desired effect, the guidance system generally obtains information relating to the actual trajectory, compares the actual trajectory to the desired trajectory, and actuates at least one control surface to direct the ordnance delivery device in a certain manner. To coordinate these tasks, a guidance system generally includes an electronic control system, whether physically connected to the ordnance delivery device or in communication with it.
In summary, there are many possible designs for building a guidance system. Obtaining information pertinent to calculation of the actual trajectory generally requires an information gathering device selected from at least one of many possibilities. Further, the actuation of the control surface may be performed by a variety of mechanisms. In addition, the desired effects are various. Given this complexity, the approach to constructing an electronic control system has generally been the implementation of unique electronic control system for each combination of information gathering devices, control surface mechanisms, and desired effects.